PersontoPerson Microbial Diseases

1
Chapter 26

• Person-to-Person Microbial Diseases

2
Airborne Pathogens

• Air is not a suitable medium for growth of
  microorganisms organisms found in the air are
  derived from the soil, water, plants, animals,
  people, etc.
• Some species can survive travel by air, ex.
  species found in the upper respiratory tract,
  even pathogenic species of Staphylococcus and
  Streptococcus.
• Avg. human breathes 500 million liters of air in
  a lifetime, much of it containing
  microorganism-laden dust, which can cause
  respiratory infections.
• Respiratory pathogens include streptcoccal
  diseases, diphtheria, whooping cough,
  tuberculosis, meningitis, and viral infections
  (cold, flu, etc.)

3
Streptococcal Diseases

• Nonsporulating, aerotolerant or anaerobic, gram
  cocci.
• Potent human pathogens S. pyogenes and S.
  pneumoniae.

4
Streptococcus pyogenes

• S. pyogenes ? strep throat, although it can exist
  as normal flora
• Can also cause tonsilitis, ear infections, etc.
• ?-hemolytic on BA.
• Treatable with antibiotics.
• Some strains can cause scarlet fever due to a
  phage-encoded exotoxin.
• Some strains can also cause rheumatic fever ?
  tissue destruction of organs, joints, etc.,
  causes autoimmune reaction.
• Diagnosed using rapid antigen detection (Ag) ?
  surface Ags from throat swab extracted and
  reacted with Abs.

5
Streptococcus pneumoniae

• Encapsulated
• Causes lung infections that often occur as
  secondary infections
• Cells invade lower respiratory tract
• Has fatality rate of 30
• Can also cause other types of infections

6
Corynebacterium ? Diphtheria

• Causes diphtheria severe respiratory disease,
  usually infects children.
• Previous infection or immunization provides
  complete resistance to infection.
• Forms pseudomembrane on throat that can block the
  passage of air.
• Diphtheria toxin can cause systemic damage to
  major organs.

7
Bordetella ? Whooping Cough

• Bordetella pertussis ? pertussis exotoxin and an
  endotoxin.
• Highly infective respiratory disease often
  occurring in young children.
• Violent whooping cough can last 6 weeks.
• Diagnosed by culturing or fluorescent Ab test.
• Vaccination available to children at specific
  intervals, and not completely effective.

8
Mycobacterium ? Tuberculosis

• Acid-fast bacillus transmitted by respiratory
  route.
• Results in primary and post-primary infection.
• Causes delayed type hypersensitivity resulting in
  the formation of tubercles (aggregates of
  activated macrophages) visible in the lungs by
  chest x-ray after chronic infection.
• Tested for by tuberculin test protein fraction
  from the organism is injected under the skin and
  elicits a localized immune reaction in
  individuals within 3 days.
• Treatment lasts for 9 months.

9
Mycobacterium leprae ? leprosy (Hansens disease)

• The only Mycobacterium species that has not been
  grown on artificial media.
• Forms bulblike lesions on the skin, which contain
  up to 109 bacterial cells/gram of tissue.
• Lesions can be disfiguring and cause neural
  damage.
• Treatment lasts for 1 yr.

10
Mycobacterium bovis

• Pathogenic in humans and animals.
• Enters humans via intestinal tract from raw milk.
• Causes symptoms similar to tuberculosis.
• Pasteurization of milk and eradication of
  diseases cattle have eliminated transmission of
  the disease from cattle to humans.

11
Neisseria meningitidis ? meningitis

• Meningitis inflammation of meninges membranes
  lining the CNS.
• normal flora for up to 30 of individuals.
• Affects populations in close quarters, ex.
  military, college dorms.
• Cultured on Modified Thayer-Martin medium.
• Causes rapid onset of life-threatening symptoms.
• Immunization is available.
• Staphylococcus, Streptococcus, or Haemophilus
  influenzae also cause meningitis.

12
Viruses ? Respiratory Infections

• Viral infections more difficult to treat,
  treatments often harm host as well.
• Most viral infections are acute and
  self-limiting, but some are more serious, ex.
  smallpox, rabies, measles, mumps, rubella,
  chickenpox ? all are transmitted by respiratory
  route and vaccines are available.

13
Measles, Mumps, Rubella, Chickenpox

• Measles is caused by paramyxovirus ?
  characteristic rash other symptoms. Can cause
  neurological disorders.
• Mumps is caused by another paramyxovirus. Can
  cause encephalitis and sterility.
• Rubella (German measles) is caused by ssRNA
  togavirus. Symptoms similar to measles, but
  milder. Can infect fetus of infected mother,
  causing serious abnormalities.
• Chickenpox and shingles are caused by varicella
  virus. Highly contagious, can cause disfiguring
  marks, remains dormant in nerve cells for years
  and can erupt later as painful shingles.

14
Colds

• Colds and flu most common infectious diseases.
• Estimates suggest that each person averages more
  than 3 colds per year over a lifetime!
• Colds are caused by ssRNA rhinovirus.
• Symptoms rhinitis (inflammation of nasal
  region), nasal obstruction, watery nasal
  discharges, general malaise, usually without
  fever ? treat with antihistamine, decongestant,
  and pain reliever.

15
Influenza

• Flu is caused by ssRNA influenza virus.
• Undergoes reassortment of genes called antigen
  shift and antigenic drift due to mutations.
• Symptoms low-grade fever for 3-7 days, chills,
  fatigue, headache and body aches.
• Flu vaccines are a combination of antigens from
  strains that are predicted to predominant during
  a given flu season.
• Can result in secondary bacterial infections.
• Treatment with antiviral agents is available at
  the beginning of the infection.

16
Staphylococcus

• Can exist as normal flora and can cause
  life-threatening disease. Cause common
  infections of skin and wounds.
• Gram-pos. cocci.
• 2 potential pathogens S. aureus and S.
  epidermidis, which can inhabit the skin and upper
  respiratory tract.
• Transmitted by direct contact.
• Many diseases are suppurative pus-forming.
• Can produce hemolysins, coagulase, leukocidin.
• Strains of S. aureus can cause TSS (whats this?)
  due to exotoxin production.
• S. epidermidis can cause food poisoning.
• Staphylococci often cause nosocomial infections
  (what are these?), including drug-resistant
  infections.

17
Helicobacter pylori ? Gastric Ulcers

• Gram-neg., motile, able to withstand pH 2 of
  stomach, causing ulcers.
• Mode of transmission not established but
  suspected to occur through direct contact or
  contaminated food/water.
• Abs do not protect or prevent colonization.
• Usually results in chronic infection, but can be
  treated with antibiotics (long-term treatment is
  required).

18
Hepatitis Viruses

• Hepatitis liver inflammation causes by
  infectious agent ? destruction of liver
  cirrhosis ? liver cancer. Symptoms fever,
  jaundice, liver enlargement, abnormal levels of
  liver enzymes, cirrhosis.
• Hepatitis A virus transmitted person-to-person
  or through contaminated food/water, vaccine
  available.
• Hepatitis B virus transmitted by parenteral
  route (whats this?), vaccine available.
• Hepatitis C virus also transmitted
  parenterally, up to 85 of individuals develop
  chronic hepatitis.
• There is also a Hepatitis D, E, and G.

19
Gonorrhea

• STD, caused by Neisseria gonorrhoeae.
• Gram-neg. diplococcus, sensitive to drying, and
  transmitted only by person-to-person contact.
• Symptoms can vary in males and females and may be
  so mild that they are mistaken for other types of
  infections.
• Causes eye infections in newborns, so all
  newborns are treated prophylactically.
• Can be treated with antibiotics, though many
  strains resistant to penicillin.
• Incidence remains high because 1. Acquired
  immunity does not exist, so repeated infection is
  possible, 2. Oral contraceptives causes females
  to be more easily colonized, 3. Symptoms in
  female can be so mild that they are
  unrecognizable.

20
Syphilis

• Caused by a spirochete, Treponema pallidum, which
  is very sensitive to drying and can be viewed by
  darkfield microscopy.
• Can be passed from mother to fetus, causing
  congenital syphilis.
• Primary lesion chancre, formed within 2 weeks
  to 2 months.
• Disease can enter secondary and even tertiary
  stages ? fatal infections of cardivascular system
  or CNS.
• Penicillin effective treatment.

21
Chlamydia

• Caused by Chlamydia trachomatis ? most prevalent
  cause of venereal disease.
• Can be transmitted to newborn from infected
  mother.
• Causes PID in females ? can cause infertility.

22
Herpes

• Caused by herpes simplex viruses, which cause
  painful blisters
• HSV-1 ? infects epithelial cells of mouth and
  lips ? cold sores and fever blisters.
• HIV-2 ? associated with genital region ?
  incurable, can cause cervical cancer, blisters
  may be controlled by acyclovir.

23
Trichomoniasis

• Caused by protozoan Trichomonas vaginalis.
• Transmitted by primarily by sexual contact, but
  can also be transmitted by contaminated toilet
  seats, sauna benches, and paper towels.
• Infects males (asymptomatic) and females (vaginal
  discharge, vaginitis, painful urination).
• Up to 50 of sexually active females infected,
  but only 5 of males are infected.
• Treatable by antiprotozoal drug.

24
HIV ? AIDS

• Recognized in 1981. Since then 800,000 cases
  reported in U.S. and 400,000 deaths. Worldwide
  50 million infected, 16 million have died.
• 2 types HIV-1 (99 of cases) and HIV-2 (West
  African strain).
• Caused by human immunodeficiency virus
  retrovirus (ssRNA).
• Definition of AIDS 1. CD4 T cell less than
  200 /mm3 (normal is 600 min.) or less than 14 of
  all lymphocytes, or 2. Have any one of a of
  secondary infections characteristic of AIDS
  patients, ex. Kaposis sarcoma, Pneumoncystis
  carinii pneumonia most common, etc.

25
HIV/AIDS (cont.)

• Cell Interactions HIV infects cells with CD4
  surface protein, which can include B cells,
  certain brain and intestinal cells, but most
  commonly macrophages and T helper cells. HIV
  also needs CCR5 receptor to cause infection and
  AIDS people without this receptor dont get HIV
  infection/AIDS (this is extremely rare!). HIV
  ends up causing the systematic destruction of
  macrophages and T cells (CD4 70 of total),
  leading to a catastrophic breakdown of immunity.
• Infection Following reverse transcription, the
  viral cDNA integrates into the host chromosomal
  DNA where it exists as a provirus, remaining
  latent for long periods. T cells producing HIV
  no longer divide and eventually die. Eventually
  all other lymphocyte production is shut down and
  the immune system is destroyed. AIDS patients
  die of opportunistic infections.

26
HIV/AIDS (cont.)

• Treatments treat HIV-specific proteins
  reserve transcriptase inhibitors, protease
  inhibitors.
• Diagnosis/Detection usually detect Ab to HIV,
  not virus itself to see if someone is HIV or -.
  Need 2 tests to confirm initial neg. result
  since Ab take time to be produced. False pos.
  results and/or lab mixups have also occurred.
  Can also detect actual viral load with RT-PCR
• Immunization Genetic variability of HIV has
  hampered the development of an AIDS vaccine.
  Possible vaccines include subunit vaccines,
  killed intact HIV, or live attenuated virus.